Conference calls are used in many situations nowadays. They are of particular use to groups of people who need to reach a decision rapidly but cannot talk face to face. By using a conference call a single number may be dialed to set up a conference call. This negates the need to make multiple individual calls or even connect multiple parties on an individual basis to a conference call. In the emergency services this can prove especially important where informed decisions need to be made rapidly.
There are presently three main ways of setting up a conference call in a Global System for Mobile Communication (GSM) or General Packet Radio Service (GPRS) network. Firstly, a call may be set up such that each user connects to the call using a respective channel on the network; a so called “Multiparty Bridge” call. The use of one channel per user rapidly uses up bandwidth meaning that only a limited number of users within a certain area can participate in the group call using this type of conference call technique. However, this type of multi-party call is highly efficient when contacting users who are distributed over a large geographic area and who are therefore served by many different base stations.
The second method for setting up a conference call involves defining an area over which the call is to be available and providing only one channel for that call in each cell within that area. This may be provided in cells which use GSM Phase 2+ with Advanced Speech Call Items (ASCI). Any users in a cell within the predefined area and subscribed to be part of the conference call can connect to the channel and take part in the conference call. However, any subscribed users not within one of the cells contained by the predefined area cannot take part in the call as they have no channel allocated to allow them to take part in the conference call. Additionally, there is a significant cost associated with upgrading many handsets, base stations and the provider infrastructure to the GSM Phase 2+ standard to provide the ASCI capability. Hence, there is the possibility that people who need to be included in the conference call are not. Nevertheless, this is an efficient way of providing a conference call if there are a large number of users within a small geographical area.
The final method for setting up a conference call is known as Push-to-talk (PTT). This method uses a packet switched network and, as with the multi-party bridge call set up, one channel is allocated to each user resulting in the same drawbacks. However, there are additional disadvantages to this method of conference calling in that, at present, the system is not considered robust enough to be relied on for emergency service calls and requires further development.
For the Emergency Services a typical scenario could be that, at the beginning of an emergency situation, members of the Emergency Services are widely dispersed. Then, as the emergency progresses, more members are likely to converge on a single area. There is currently no efficient method for providing a multiparty call to people involved in a scenario such as this.